Spot-knocking method for electronic tubes

ABSTRACT

For spot-knocking a cathode ray tube including a first electrode adapted to be externally applied with a high operating voltage, a high voltage in excess of the operating voltage is supplied across the electrode and ground to cause an electric discharge within the tube while a second electrode disposed adjacent the first electrode between it and a cathode is connected to ground through a resistor. This leads to a flow of current through the resistor to cause another electric discharge across the second electrode and a third electrode adjacent it and grounded.

United States Patent [191 Nakanishi et al.

[451 May 29,1973

1 1 SPOT-KNOCKING METHOD FOR ELECTRONIC TUBES [75] Inventors: Hisao Nakanishi; Wataru Imanishi,

both of Kyoto, Japan [73] Assignee: Mitsubishi Kenki Kabushiki Kaisha,

Tokyo, Japan [22] Filed: Mar. 26, 1971 [21] Appl. No.: 128,294

[52] US. Cl. ..316/26, 29/25.]1, 316/1 [51] Int. Cl ..H0lj 9/00 [58] Field of Search ..29/25.1, 25.11; 316/26, 22, l

[56] References Cited UNITED STATES PATENTS 2,073,190 3/1937 Bartlett et a1 ..29/25.l X 2,952,499 9/1960 Carson ..3l6/26 X Palac ..3 16/1 Javorik .316/26 Primary Examiner-J. Spencer Overholser Assistant Examiner-Richard Bernard Lazarus Attorney-Robert E. Burns and Emmanuel J. Lobato 5 7 ABSTRACT For spot-knocking a cathode ray tube including a first electrode adapted to be externally applied with a high operating voltage, a high voltage in excess of the operating voltage is supplied across the electrode and ground to cause an electric discharge within the tube while a second electrode disposed adjacent the first electrode between it and a cathode is connected to ground through a resistor. This leads to a flow of current through the resistor to cause another electric discharge across the second electrode and a third electrode adjacent it and grounded.

10 Claims, 1 Drawing Figure SPOT-KNOCKING METHOD FOR ELECTRONIC TUBES BACKGROUND OF THE INVENTION This invention relates to a method of improving the high voltage stability or withstand-voltage characteristic of electron tubes such as cathode ray tubes having high voltages applied thereto.

in the field of electron tubes such as cathode ray tubes having a high voltage applied thereto, it is well known that when the high voltage stability is had between any of the electrodes and the tubular member of the enclosure for the electronic tube, a useless electric discharge or stray emission is caused therebetween leading to the deterioration of the function of the elec tronic tube. Also it is commonly known that the adhesion of foreign or contaminative matters to the electrodes and/or the tubular enclosure portion forms a source of effecting such an electric discharge or stray emission. ln order to eliminate the source of stray emission, it is commonly practiced to apply to electron tubes a high voltage between several times and scores of the normal operating voltage therefor to force the electron tubes to cause the electric discharge therein whereby the source becomes extinct by means of an electrical energy due to that electric discharge. This is known as the so-called spot-knocking technique which will be subsequently described in conjunction with a color, bipotential cathode ray tube including a first, a second, a third and a fourth electrode disposed in the named order starting with the side of the front face plate of the tube for the purpose of focussing a beam of electrons generated by a cathode electrode.

It is assumed that such a cathode ray tube is used as a commercial television picture tube. Under the assumed condition, with respect to thecathode electrode held at a potential approximating the ground potential, the first electrode is kept at a high voltage of about 27 kilovolts, thesecond electrode at an auxiliary high voltage of about 3.5 kilovolts, the third electrode at a voltage of about 300 volts and the fourth electrode is kept at a voltage of about minus 75 volts. Therefore it is required to maintain the high voltage stability particularly between the first electrode and second electrode, between the third electrode and second electrode, and between the first and second electrodes and that portion not applied with an electrically conductive coating of the tubular enclosure member decreased in diameter.

With cathode ray tubes having the construction such as above described, it is well known in the art that the spot-knocking technique as above described can be conducted with the first electrode applied with a high voltage equal to several times the operating voltage therefor with respect to a common voltage applied to the second, third, fourth .and cathode electrodes and the associated heater element connected together. That high voltage may be, for example, nearly 50 to 60 kilovolts for the cathode ray tube as above described. Under these circumstances, the.spot-knocking operation has never been performed between the second and third electrodes and between the second electrode and that portion located adjacent the second electrodes of the tubular enclosure member. This has resulted in the disadvantage that the withstand voltage characteristic is not improved around the components just described.

As above described, the spot-knocking operation has been previously performed with the second and third electrodes held at the same potential for the following reasons. Firstly, in order to render the spot-knocking operation effective between the second and third electrodes, it is required to apply to the second electrode a high voltage equal to several times the operating voltage therefor with respect to the third electrode and in fact through the associated lead-in conductor from an external source of voltage. In that case electric discharges will occur between that lead-in conductor and the adjacent lead-in conductors and between that portion of the first-mentioned lead-in conductor disposed within the interior of the tubular enclosure member and connected to the second electrode and electrodes disposed adjacent that conductor portion with the result that no spot-knocking operation is performed between the second electrode and the third electrode opposite to the latter. In order to render the spotknocking effective between the second and third electrodes, it becomes necessary to take special measures in designing and producing those electrodes leading to a want of economy. Secondly, in order to perform the spot-knocking operation satisfactorily between the first and second electrodes, it is required to superpose the high voltage applied to the second electrode upon the high voltage appliedto the first electrode. This leads to the necessity of taking a special step of forming a conduction path extending from the first electrode to the associated anode button and therefore to a want of economy. Particularly for cathode ray tubes commer- I cially available for television purpose, it is required to provide means for protecting persons engaged in producing such tubes from dangers and injuries due to the leaked X ray resulting from the application of such a high voltage to the first electrode. This causes an increase in want of economy.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide an improved method of spot-knocking electronic tubes whereby any source of causing the stray emission within the electronic tubes can disappear to thereby improve the high voltage stability.

It is another object of the invention to provide a simplified means for readily carrying out the spotknocking method as described in the preceding paragraph.

It is still another object of the invention to provide a spot-knocking method particularly effective for producing bipotential type cathode ray tubes.

The invention accomplishes these objects by the provision of a method of spot-knocking an electronic tube including a cathode electrode capable of emitting a beam of electrons, a firstelectrode disposed in the direction in which the beam of electrons is emitted from the cathode electrode and'capable of being externally applied with a high voltage, and a second electrode, a third electrode and a fourth electrode disposed in opposite relationship between the first electrode and the cathode electrode, whichmethod comprises the steps of connecting the second electrode to ground through a resistor while the third electrode, and the fourth electrode directly connected together to ground, and applying a high voltage in excess of the operating voltage 9 for the first electrode across the first electrode and ground thereby to cause an electric discharge across the first electrode and the second electrode adjacent it while causing a current due to the electric discharge to flow through the resistor thereby to effect another electric discharge. between the second electrode and the third electrode.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, there is illustrated a bipotential type cathode ray tube including an enclosure 1 formed of any suitable transparent material such as glass into a circular tube including a flared portion at one end and closed at the other end. The flared portion is closed by a front face plate and the interior of the enclosure is maintained in a high vacuum. The flared enclosure portion is provided on the internal surface with an electrically conductive coating 2 which, in turn, extends slightly upon the internal wall surface of that portion of the tube contiguous to the flared enclosure portion. Then an anode button 3 is disposed on the flared portion of the enclosure 1 to be electrically connected to the conductive coating 2.

Within the tubular member decreased in diameter of the enclosure 1 there are disposed a first electrode 4 I adjacent that end thereof adjacent the flared enclosure portion and a cathode electrode 5 adjacent the opposite end thereof. Disposed between the first and cathode electrodes 4 and 5 respectively and within the tubular enclosure portion are a second, a third and a fourth electrode 6, 7 and 8 respectively in spaced opposite relationship and in the named order starting with the side of the first electrode 4. All the electrodes are located coaxially to one another and to the tubular enclosure portion by means of two or three beaded rods 9 of glass.

The first electrode 4 is adapted to be externally applied with a high voltage through the anode button 3, the conductive coating 2 and a lead connecting the same to the conductive coating 2. The second electrode 6 is connected by a lead to a lead-in conductor 10 sealed through the closed end of the tubular enclosure portion to be externally applied with an auxiliary high voltage less than the voltage applied to the first electrode and the third, fourth and cathode electrodes 7, 8 and 5 respectively are connected by leads to the associated lead-in conductors ll, 12 and 13'also sealed through the closed end of the tubular enclosure portion respectively for the purpose of externally applying the respective voltages thereto/The cathode electrodeS encircles a heating element 14 connected at both ends closed end of the tubular enclosure portion respec The cathode ray tube as above described is of the conventional construction and need not be described in detail.

According to the principles of the invention, a resistor -16 is connected at one end to the lead-in conductor 10 connected to the second electrode 6 and at the other end to the lead-in conductors 11, 12, 13 and 15 connected to the third, fourth and cathode electrodes 7, 8 and 5 and the heating element 14 respectively and also to ground. A source of high voltage 17 having a negative side connected to ground applies to the first electrode 4 a high voltage required to perform the normal spot-knocking operation. This high voltage may be preferably of from 50 to 60 kilovolts for the cathode ray tube shown in the drawing. Upon performing the spot-knocking operation, no occurrence of an electric discharge within the enclosure 1 causes the second electrode 6 to be at the ground potential so that the high voltage for example of from 50 to 60 kilovolts applied to the first electrode 4 is maintained across the first and second electrodes 4 and 6 respectively.

Upon an electric discharge occurring across the first and second electrodes 4 and 6 respectively, the spotknocking operation is performed therebetween while at the same time a current due to that electric discharge flowsthrough the resistor 16. This flow of current through the resistor 16 permits the potential at the second electrode 6 to be raised by a value determined by the product of the value of the discharge current multiplied by the value of resistance 16. Therefore the spotknocking operation is also performed between the second and third electrodes 6 and 7.

If desired, the cathode electrode 5 may be applied with a positive potential rather than with the ground tively. The heating element 14 is adapted to be externally supplied witha current through the lead-in conductors 15 to heat the cathode electrode 5 to permit the thermoionic emission to'be effected toward the electrodes 8, 7 and 4 therefrorn; I I

potential.

In this connection it is'to be noted that the magnitude of the resistance 16 should be preselected to provide a voltage required to perform the spot-knocking operation between the second and third electrodes. It has been found that as an example, the resistor 16 having a magnitude of resistance of 200 kilohms has induced thereacross a voltage of about 10 kilovolts with the result that the cathode ray tube has been much improved in high voltage stability. However, it is to be understood that the invention should not be restricted to the value of resistance just specified.

For demonstrating the effect of the invention, experiments were conducted with bipotencial type cathode ray tubes such as shown in the drawing. In the experiments, the fourth electrode was at l50 volts and the third and first electrodes were at 200 volts and 30 kilovolts respectively while the second electrode was selectively put at 0, 4, 6 and 8 kilovolts for determining whether or not the stray emission would occur in the tubes. The results of the experiments are listed in the following Table I.

TABLE I Voltage Applied to Second Electrode in kv. Tube No. 0 4 6 8 1 o o o o 2 x o o o 3 o o o o 4 o o o o 5 o o o o 6 o o o o 7 o o o o 8 x x o o 9 o o o o 10 o o o o l 1 o o o o 12 x o o 13 o 0 0 o 14 o o o o 15 o o o o In the above Table l, the symbol circle (0) indicates that the stray emission did not occur while the symbol cross (x) indicates that the stray emission occurred.

From the Table l it is apparent that for the voltage of 0 or 4 kilovolts applied to the second electrode, a few tubes had the stray emission occurring therein whereas for the voltage of 6 or 8 kilovolts applied to the second electrode, none of the tubes had the stray emission occurring therein. This offers a proof that the spotknocking method according to the invention is superior to the conventional spot-knocking methods.

If desired, the resistor 16 may have a capacitor 18 connected in parallel thereto as shown at dotted line in the drawing. In the absence of the capacitor 18, a duration for which a voltage is developed across the resistor 16 is restricted to an instant an electric discharge occurs. However in the parallel combination of resistor and capacitor, an electric energy due to an electric discharge is temporarily accumulated by the capacitor 18 to sustain the spot-knocking operation performed between the second and third electrode 6 and 7 respectively for a duration determined by the time constant of the resistor 16 and the capacitor 18, leading to a great improvement in high voltage stability.

While the invention has been described in conjunction with a few preferred embodiments thereof, it is to be understood that various changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, the capacitor 18 may be replaced by a stray capacitance between connecting leads to the resistor 16 and connecting leads for connecting the remaining electrodes to ground. Also while the invention has been described in terms of the bipotential type cathode ray tube, it is equally applicable to unipotential type cathode ray tubes and other electronic tubes.

What we claim is:

1. A method of spot-knocking an electronic tube including a cathode electrode capable of emitting a beam of electrons, a first electrode disposed in the direction in which the beam of electrons is emitted from the cathode electrode and capable of being externally applied with a high voltage, and a second electrode, a third electrode and a fourth electrode disposed in opposite relationship between said first electrode and said cathode electrode, which method comprises the steps of connecting said second electrode to ground through a resistor while said third electrode and said fourth electrode are directly connected together to ground, and applying a high voltage in excess of the operating voltage for said first electrode across said first electrode and ground thereby to cause an electric discharge across said first electrode and said second electrode while causing a current due to said electric discharge to flow through said resistor thereby to cause another electric discharge across said second and third electrodes.

2. A spot-knocking method as claimed in claim 1, wherein said resistor has a capacitor connected in parallel circuit relationship thereto.

3. A spot-knocking method as claimed in claim 1, wherein said resistor has operatively coupled thereto a stray capacitance formed of external conductors connected to the electron tube.

4. A method of spot-knocking a bipotential type electronic tube including a cathode electrode capable of emitting a beam of electrons, a first electrode disposed in the direction in which the beam of electrons is emitted from cathode electrode and capable of being externally applied with a high voltage, and a second electrode, a third electrode and a fourth electrode disposed in opposite relationship between said first electrode and said cathode electrode, said second electrode being positioned adjacent said first electrode and capable of being externally applied with an auxiliary high voltage less than the operating voltage for the first electrode, which method comprises the steps of connecting said second electrode to ground through a resistor while said third electrode and said cathode are directly connected together to ground, and applying a high voltage in excess of the operating voltage for the first electrode across said first electrode and ground thereby to cause an electric discharge across said first electrode and said second electrode while causing a current due to said electric discharge to flow through said resistor to effect another electric discharge across said second electrode and said third electrode.

5. A method of spot-knocking an electronic tube having a cathode electrode for emitting a beam of electrons during use of the tube and a set of focussing electrodes disposed in mutually spaced-apart relationship along the direction of electron beam emission for focussing the electron beam during use of the tube including a first electrode disposed farthest from said cathode electrode and second, third and fourth electrodes disposed in that order between said first electrode and said cathode electrode, the method comprising: applying a voltage in excess of the normal operating voltage for the tube to said first electrode to simultaneously effect both a primary electric discharge across said first and second electrodes and a secondary electric discharge across said second and third electrodes.

6. A method according to claim 5; wherein said applying step comprises applying said voltage to said first electrode to effect said primary electric discharge and developing therefrom a potential difference across said second and third electrodes having sufficient magnitude to create said secondary electric discharge thereacross.

7. A method according to claim 5; wherein said step of developing a potential difference comprises developing a voltage drop from the current flowing due to said primary electric discharge having sufficient magnitude relative to the voltage of said third electrode to establish said potential difference across said second and third electrodes.

8. A method according to claim 7; wherein said step of developing a voltage drop from the current comprises flowing said current through a given resistor to develop thereacross said voltage drop 9.'A method according to claim 8; including sustaining the duration of said secondary electric discharge for a predetermined duration.

10. A method according to claim 9; wherein said sustaining step comprises connecting a capacitor in parallel with said given resistor whereby said predetermined time period is determined by the time constant of said given resistor and capacitor. 

1. A method of spot-knocking an electronic tube including a cathode electrode capable of emitting a beam of electrons, a first electrode disposed in the direction in which the beam of electrons is emitted from the cathode electrode and capable of being externally applied with a high voltage, and a second electrode, a third electrode and a fourth electrode disposed in opposite relationship between said first electrode and said cathode electrode, which method comprises the steps of connecting said second electrode to ground through a resistor while said third electrode and said fourth electrode are directly connected together to ground, and applying a high voltage in excess of the operating voltage for said first electrode across said first electrode and ground thereby to cause an electric discharge across said first electrode and said second electrode while causing a current due to said electric discharge to flow through said resistor thereby to cause another electric discharge across said second and third electrodes.
 2. A spot-knocking method as claimed in claim 1, wherein said resistor has a capacitor connected in parallel circuit relationship thereto.
 3. A spot-knocking method as claimed in claim 1, wherein said resistor has operatively coupled thereto a stray capacitance formed of external conductors connected to the electron tube.
 4. A method of spot-knocking a bipotential type electronic tube including a cathode electrode capable of emitting a beam of electrons, a first electrode disposed in the direction in which the beam of electrons is emitted from cathode electrode and capable of being externally applied with a high voltage, and a second electrode, a third electrode and a fourth electrode disposed in opposite relationship between said first electrode and said cathode electrode, said second electrode being positioned adjacent said first electrode and capable of being externally applied with an auxiliary high voltage less than the operating voltage for the first electrode, which method comprises the steps of connecting said second electrode to ground through a resistor while said third electrode and said cathode are directly connected together to ground, and applying a high voltage in excess of the operating voltage for the first electrode across said first electrode and ground thereby to cause an electric discharge across said first electrode and said second electrode while causing a current due to said electric discharge to flow through said resistor to effect another electric discharge across said second electrode and said third electrode.
 5. A method of spot-knocking an electronic tube having a cathode electrode for emitting a beam of electrons during use of the tube and a set of focussing electrodes disposed in mutually spaced-apart relationship along the direction of electron beam emission for focussing the electron beam during use of the tube including a first electrode disposed farthest from said cathode electrode and second, third and fourth electrodes disposed in that order between said first electrode and said cathode electrode, the method comprising: applying a voltage in excess of the normal operating voltage for the tube to said first electrode to simultaneously effect both a primary electric discharge across said first and second electrOdes and a secondary electric discharge across said second and third electrodes.
 6. A method according to claim 5; wherein said applying step comprises applying said voltage to said first electrode to effect said primary electric discharge and developing therefrom a potential difference across said second and third electrodes having sufficient magnitude to create said secondary electric discharge thereacross.
 7. A method according to claim 5; wherein said step of developing a potential difference comprises developing a voltage drop from the current flowing due to said primary electric discharge having sufficient magnitude relative to the voltage of said third electrode to establish said potential difference across said second and third electrodes.
 8. A method according to claim 7; wherein said step of developing a voltage drop from the current comprises flowing said current through a given resistor to develop thereacross said voltage drop.
 9. A method according to claim 8; including sustaining the duration of said secondary electric discharge for a predetermined duration.
 10. A method according to claim 9; wherein said sustaining step comprises connecting a capacitor in parallel with said given resistor whereby said predetermined time period is determined by the time constant of said given resistor and capacitor. 